System and Method for Heating

ABSTRACT

A gas furnace is provided. Embodiments of the present disclosure generally relate to a gas furnace operated such that the flame temperature is maximized by ensuring operation at or near stoichiometric conditions. Additional systems, devices, and methods are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of U.S. Provisional Patent Application No. 62/688,404, entitled “System and Method for Heating,” filed on Jun. 22, 2018, and which is herein incorporated by reference in its entirety.

BACKGROUND

This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the presently described embodiments—to help facilitate a better understanding of various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Modern residential and industrial customers expect indoor spaces to be climate controlled. In general, heating, ventilation, and air-conditioning (“HVAC”) systems circulate an indoor space's air over low-temperature (for cooling) or high-temperature (for heating) sources to adjust the indoor space's ambient air temperature. For cooler climates, heating is often provided by gas furnaces that combust a gaseous fuel (e.g., methane, propane) to generate heat that is “blown” into the indoor space.

In North America, a gas furnace's efficiency is often described through its annual fuel utilization efficiency (AFUE) rating, which is a ratio of a furnace's useful energy output to its energy input and is expressed as a percentage. For example, a furnace with an AFUE rating of 80 theoretically generates 80 British thermal units (BTUs) of heat for every 100 BTUs of natural gas input. But this AFUE rating is derived from certain assumed coefficients pursuant to Standard 103, which is promulgated by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

A gas furnace's actual effectiveness or efficiency is a primarily based on two factors: 1) the amount of heat generated during combustion of a given amount of fuel and 2) the amount of that generated heat that can be transferred (i.e., exchanged) into the ambient air being “blown” through the furnace. And a furnace that improves one or both of these aspects can be more efficient even if that furnace's AFUE is unaffected.

SUMMARY

Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.

Embodiments of the present disclosure generally relate to a gas furnace with improved efficiency and operational characteristics. In one embodiment, the flame temperature is increased by controlling an airflow inducer to optimize the heat produced by a flame. In another embodiment, the furnace's efficiency is improved via a balancing plate that controls the airflow induced across the gas furnace's burners. In a further embodiment, the gas furnace includes turbulence generating features that affect the characteristics of the furnace's generated flame. Advantageously, certain disclosed embodiments may provide a furnace that while having a derived AFUE rating of 80 may present the same or better efficiency as another furnace having an AFUE rating of 90.

Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates schematically an HVAC system for heating and cooling indoor spaces within a structure, in accordance with an embodiment of the present disclosure;

FIG. 2 is a schematic, side view of a gas furnace, in accordance with an embodiment of the present invention;

FIG. 3 is a schematic, front view of a gas furnace, in accordance with an embodiment of the present invention;

FIG. 4 is an isometric view of a primary heat exchanger for a furnace, in accordance with one embodiment of the present invention;

FIG. 5 is a schematic, top view of a balancing plate for a furnace, in accordance with one embodiment of the present invention; and

FIG. 6 is a schematic view of a burner and primary heat exchanger for a furnace, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Turing now to the figures, FIG. 1 illustrates an HVAC system (10) in accordance with one embodiment. As depicted, the system (10) provides heating and cooling for a residential structure (12). But the concepts disclosed herein are applicable to a myriad of heating and cooling situations, including industrial and commercial settings. To effect heating and cooling, heat exchangers of an outdoor unit (14) and an indoor unit (18) cooperate to take advantage of a well-known physical principle: A fluid transitioning from gas to liquid releases heat, while a fluid transitioning from liquid to gas absorbs heat. The system circulates fluid refrigerant through a closed loop of tubing (20). And by manipulating the refrigerant's flow and pressure, the refrigerant cycles between the liquid and gas phases. The indoor unit's heat exchanger (e.g., an A-coil (16)) may act as an evaporator to facilitate the refrigerant's transition from liquid to gas, causing the refringent to absorb ambient heat. Or the A-coil (16) may act as a condenser to facilitate the refrigerant's transition from gas to liquid, causing the refringent to release heat to the ambient air. Whatever the state of the A-coil—condenser or evaporator—the outdoor unit's heat exchanger will be in the opposite state, either releasing heat to or absorbing heat from the environment.

To take advantage of the A-coil's absorption of heat from or release of heat to the ambient air, the indoor unit (18) has a blower assembly (22) that—in cooperation with ducts or ductwork (24)—provides airflow circulation by drawing in ambient air from the indoor spaces (26), passing it over the A-coil (16) to either heat or cool that ambient air, and returning the ambient air to the indoor space (26) after being conditioned.

But in cooler climates or in areas where natural gas is relatively inexpensive, heating may be provided or supplemented by a gas furnace (28) that combusts a gaseous fuel, such as natural gas, to produce heat. Ambient air circulated by the blower (22) is then “blown” or passed over a heat exchanger in the furnace, raising the temperature of the ambient air circulating back into the indoor spaces (26).

FIGS. 2 and 3 illustrate a gas furnace (28). Heat is generated by one or more gas burners (30) fed natural gas via a gas manifold (32)—with a gas valve (34) controlling the amount and rate of natural gas introduced into the manifold from a gas source (not shown). Advantageously, the gas valve (34) may be a variable or multistage valve that can dynamically control the amount and rate of gas delivered to the manifold (32). For example, the illustrated gas valve (34) is in communication with a controller (36) that has a processor (38) and memory (40) that cooperate to provide control signals to the gas valve (34). And those signals may operate the valve at a first lower stage, a second higher stage, or a variable stage that is adjustable to a point virtually anywhere between the first and second stages—to control the amount of gas delivered to the manifold (32).

Gas from the manifold is routed to and ignited in the burners 30, thereby generating heat. Specifically, the burners (30) manage a flame (42) that heats air residing within a primary heat exchanger (44) and, in certain embodiments, a secondary heat exchanger (46). An inducer fan (48) coupled to the outlet of the heat exchangers draws air from the heat exchangers (44, 46) and into an exhaust vent (50). Advantageously, the inducer fan (48) may be a variable speed fan that receives control signals form the controller (36) to optimize the air flow within the exchangers, drawing the air heated by the flame through the heat exchangers and into the vent (50).

The heat exchangers (44, 46) cooperate with the blower (22) to increase the heat of the ambient air circulated or blown into the indoor spaces (26). Specifically, the blower (22)—which may be a variable speed blower that receives control signals from the controller (36)—blows cool ambient air over the primary and secondary heat exchangers that are carrying heated air, increasing the temperature of the ambient air that is returned to the indoor spaces (26).

The amount of heat generated by the burners (30) depends on the heat of the flame (42) produced during combustion—this heat being descried as the adiabatic flame temperature. For example, if the fuel is natural gas (e.g., methane), igniting the methane in the presence of oxygen is an exothermic reaction that generates carbon dioxide, water, and heat. But igniting methane with too little oxygen present causes incomplete combustion, which reduces the amount of heat generated by the combustion and can potentially result in the production of unwanted carbon monoxide. Moreover, incomplete combustion reduces the efficiency of the furnace because un-combusted or improperly combusted fuel expelled through the vent is BTUs of energy inputted into the furnace that are not converted to heat.

Stochiometric combustion is described in the industry as the combustion of fuel in the presence of the exact amount of oxygen needed to convert all of the gaseous fuel into carbon dioxide and water and heat. Such stochiometric combustion is said to have a fuel-to-air equivalence ratio or P of 1. While the theoretical maximum flame temperature is believed to be at a P of 1, certain dissociation effects in the fuel are believed to make the true maximum adiabatic flame temperature for a gaseous-fuel furnace at a P of 1 or slightly above 1. As an example, it is believed that the maximum flame temperature for certain types of gaseous fuel may be at a P of between 1 and 1.2—for example, 1.05 or 1.12.

Advantageously, the illustrated furnace includes one or more sensors (52)—e.g., oxygen sensors, temperature sensors, pressure sensors, fuel sensors, carbon monoxide sensors, to name but a few—that relay information regarding the combustion occurring at the burners (30) to the controller (36). In turn, the controller (36) can provide appropriate command signals to the fan (48), gas valve (34), and/or blower (22) to ensure that the proper equivalence ratio is maintained at the furnace.

In one example, the controller (36) may have a look-up table stored in memory (36) that compares the received input from the sensors to historical values, to determine the inducer fan speed and/or gas valve feed rate (firing rate) to maximize the flame temperature at the burner based on an desired equivalence ratio. In another embodiment, the controller (36) may have wired or wireless communication circuitry that enables the controller to communicate with a remote location via the internet or with a computing device, like a hand-held mobile device, computer or laptop—with such computing device, for example, providing the operation control or look-up tables. In yet another embodiment, the memory may store operational data and, over time, develop new look-up tables to ensure the highest adiabatic flame temperature for the given furnace by adjusting the equivalence ratio of the fuel air mixture at the burner.

More specifically, the controller (36) may, based on the sensed parameters from the sensors (52), reduce the inducer fan's (48) speed to ensure that an appropriate amount, based on the desired equivalence ratio and associated flame temperature, of air is being drawn into the burner. And with the flame temperature maximized, the heat output of the combustion is maximized—by keeping the combustion close to the ideal equivalence ratio. This provides for a gas furnace that can produce a maximized output of heat yet minimize the input or firing rate (input BTUs) of natural gas—making the overall furnace more efficient. Indeed, a furnace with such features may produce more heat and be more efficient than would be expected based on that furnace's calculated AFUE value. Similarly, the controller (36) may control the operation of the gas valve (34)—alone or in conjunction with the inducer fan (48)—to enable the burner to operate at the desired equivalence ratio by adjusting the amount and/or pressure of the gas provided to the gas manifold and, in turn, to the burners. In addition to efficiency, the disclosed embodiment facilitates maximized generation of heat with a lower inducer fan speed, which reduces the overall noisiness of the furnace.

In accordance with one embodiment, the overall height of the system can be reduced. For example, as illustrated in FIG. 4, the overall height of the furnace can be reduced by providing a primary heat exchanger (44) with four passes (49) but additional burners—six as shown. This also has the added benefit of increasing the surface area of the primary heat exchanger in contact with the blown ambient air, which improves the efficiency of the furnace. As another feature to increase the contact surface area, the primary heat exchanger tubing may have portions with non-circular cross-sections (45).

Turing to FIG. 5, this figure illustrates an embodiment in which the primary heat exchanger (44) is coupled to a balancing plate (54). In operation, the inducer fan (48) draws airs through the primary heat exchanger (arrows (56)) and into the vent (50). But each coiled tube (57) of the heat exchanger may feed into a plenum (58) such that the coiled tubes (57) are not equidistance from the inducer fan (48). In such case, the air flow within each tube may not be sufficient to provide the desired equivalence ratio for the burner of the given coiled tube. That is, airflow generated by the inducer fan (48) may be too high for the inner tubes (57(a) but too low for the outer tubes (57 b). To mitigate this, the balancing plate (54) has apertures (60) sized to adjust or balance the airflow through each tube (57). As illustrated, the balancing plate (54) has smaller inner apertures (60 a) that restrict the airflow through the coiled tube (57 a). By contrast, the outer tubes (57 b) have larger apertures (60 b) sized to provide greater airflow. Advantageously—through fluid modeling or direct measurements, for example—this allows each burner to have an airflow that provides an equivalence ratio closest to the desired value by adjusting the size of the aperture (60).

FIG. 6. illustrates a burner (30) and heat exchanger (44) arrangement in accordance with one embodiment. The exemplary coiled tubing (57) is coupled to an inducer fan (48) that generates airflow within the tubing. And, as discussed above, the airflow rate can be adjusted to reach the desired equivalence ratio. The illustrated coil tubing includes turbulence-inducing features—which are, in this case, dimples (62) but could be vanes, ridges or any other turbulence inducing shape. By generating turbulence, these dimples (62) help reduce the flame length produced by the burner at the desired equivalence ratio—which may be at or close to and equivalence ratio of 1. Moreover, the reduced flame length helps reduce the damage caused by the flame (42) to the coiled tube, thereby improving the furnace's durability.

While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims. For example, certain embodiments disclosed here envisage usage with a powered fan rather than an inducer fan, or no fan at all. Moreover, the rotating equipment (e.g., motors) and valves disclosed herein are envisaged as being operable at specified speeds or variable speeds through inverter circuitry, for example. Moreover, the internal and external communication of the furnace may be accomplished through wired and or wireless communicaitons, including known communication protocols, Wi-Fi, 802.11(x), Bluetooth, to name just a few. 

1. A gas furnace, comprising: a plenum in fluid communication with a fan; a heat exchanger comprising one or more tubes terminating at one end in the plenum; and a balancing plate disposed between the one end and the fan, wherein the balancing plate adjusts the airflow induced in the one or more tubes by the fan.
 2. The gas furnace of claim 1, wherein the one or more tubes comprises a turbulence inducing feature disposed on an interior surface thereof.
 3. A method for operating a furnace, the method comprising: determining a desired equivalence ratio for a gas burner; collecting combustion information from one or more sensors proximate the burner to determine the combustion properties of the burner's flame; comparing the combustion properties of the flame to expected values to determine estimated equivalence ratio; and adjusting the one or more operating parameters of the furnace if the estimated equivalence ratio deviates from the desired equivalence ratio. 